Questions of host-parasite compatibility, tissue specificity, and interactions lie at the core of scientific parasitology and are important in development of rational control methods for parasitic diseases. We are studying such relationships primarily using the snail Biomphalaria glabrata, and cell cultures derived from it, together with several species of trematode parasites. Snail tissue cultures are to be used as substrate for growth of pathogens such as viruses and protozoa, as well as for growth of sporocyst, redial, and cercarial stages of trematodes. Attention will be focused on development of cercariae of Schistosoma mansoni, an important parasite of man. Almost perfect cercariae can now be grown in appropriate cultures, but the outer water-protective glycocalyx appears lacking. We will attempt to induce production of this glycocalyx by incorporation of appropriate precursors in the culture medium. We will continue work on transformation in vivo and in vitro of cultured cercariae to the next stage, the schistosomule, and to the fully patent adult. This will be an important additional step towards the goal of completion of the entire schistosome life cycle in vitro. BIBLIOGRAPHIC REFERENCES: Basch, P.F. 1976. Parasitological Review: Intermediate host specificity in Schistosoma mansoni. Experimental Parasitology, in press. DiConza, J.J., and P.F. Basch. 1976. Cryopreservation of Biomphalara glabrata (Mollusca) cells. J. Invert. Pathol., in press.